Usually metal mosaics are porcelain backed, with a metal cap about 3mm thick, I use a carbon blade (on a dremmel) to cut through the metal then, use a grinder to cut through the porcelain. Don't try to cut them wet as the water loosens the glue and the metal cap falls off.
used the ceramic blade but it left a poor finish on the face of the tile and burnt it also the carbon blade left the same after i covered the face of the tile with tape cut again but their wasnt much difference ;what is the official technique recommended by the fabricators of these tiles;
Never thought of using my dremel, good shout bri. I normally use one of ultra thin cutting discs on my grinder, they are 1mm thick or thin depending on your take. But it can be quite tricky with the grinder. Dremel may be the way forward.